The invention relates to a pressure-balancing device for heating systems with an expansion tank which receives the heating medium, which is closed to outside air and which is connected to the heating system by feed and drain pipes, whereby a chamber of variable volume inside the expansion tank is provided.
It is known that the volume of large heating or cooling systems changes with the heating or cooling of the heating medium water. The surplus volume must be taken out of the system in the case of constant pressure, and in the case of cooling and the resulting volume decrease of the water in the system, the water must be returned to the system at the same pressure ratio.
With such heating systems it is known to deliver the water surplus caused by thermal expansion to an open reservoir and to deliver water to the system from exactly this reservoir through a pump in the case of a volume decrease.
It is of disadvantage that the heating liquid comes into contact with the outside air in the open reservoir, since this involves a substantial increase in the danger of corrosion in the system.
A pressure-balancing device is known in which the heating medium water remains separate from the outside air.
This pressure-balancing device essentially consists of a pressure tank and a group of automatic compressors which are directly mounted on the tank in small systems. In bigger systems the parts of the automatic device are placed separately.
A flange is welded to the upper and lower side of the tank whereby a rubber tube clamped between the two flanges is directly connected to the system and receives the water surplus caused by a volume increase in case of a temperature rise.
As to the construction of the tank, there is an air space between the rubber tube and the tank wall, which space is kept under pressure, i.e. under the pressure of the system, by a separate compressor. An adaptable piston manometer with limit switches controls the compressor and opens in the case of excess pressure a solenoid valve so that the pressure can constantly be kept at about .+-. 0.2 atm (1 atm = 1 kp/cm3 = 17,285 25 tr.lbs/sq in).
The function of the pressure-balancing device is as follows:
If more water of the system is delivered into the tube, air of the space between the tank wall and the tube will be blown out in order to keep a constant pressure. If the heating medium flows out of the tube, the resultant additional space in the ring slot will be filled up by air pumped in by the compressor.
The disadvantage of the known pressure-balancing device is the fact that the tank has the same pressure as the system itself.
According to Austrian regulations the tank requires a test certificate. This fact naturally entails a substantial rise in the price of the device and service therefor.